In an Effort to Study the Laser Induced Dissociation of Gas Mixtures for an Ongoing Research Project on Diamond Thin Film Coating using Multiple Lasers, It is Necessary to Determine the Absorption Coefficient of Laser Energy by CO2 Gas. an Ab Initio Molecular Dynamics (AIMD) Model is Used to Determine the Laser Absorption Coefficient of CO2 Gas as a Function of Laser Wavelength and Gas Temperature. the Translational, Rotational, and Vibration Motions of Molecules Are All Taken into Account in Our Model. the Intra-Molecular Potential Energy is Obtained by Solving the Kohn-Sham Equation. the Projector-Augmented Wave (PAW) Exchange-Correlation Potential Function is Used in the Ab Initio Calculation. Specific Heat of the CO2 Gas is Also Calculated. the Calculated Thermal Properties of CO2 Gas and the Vibration Spectrum of Molecules Are in Good Agreement with the Experimental Results. the Calculated Normalized Absorption Line Shape CO2 Gas is Close to the Experimental Results.